Dynamic Power Management (DPM) aims at minimizing energy consumption in battery-powered electronics such as mobile and embedded systems. An interesting problem under DPM is energy-optimal device scheduling that tries to minimize device energy consumption for a given task set. In this paper, we present an improved version of Energy-optimal Device Scheduler (EDS), an algorithm originally proposed by Swaminathan and Chakrabarty [8] to solve the problem for hard real-time systems. The improved algorithm cuts down execution time by as much as 99% and memory usage by up to 30% for task sets with a low execution time/period ratio. We also present a heuristic method called Device-Energy Optimizer (DEO) that attempts to find near-optimal solutions and performs remarkably well in comparison to EDS.